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WO2003016890A2 - Determining the temperature of an exhaust gas sensor by means of calibrated internal resistance measurement - Google Patents

Determining the temperature of an exhaust gas sensor by means of calibrated internal resistance measurement Download PDF

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Publication number
WO2003016890A2
WO2003016890A2 PCT/DE2002/002478 DE0202478W WO03016890A2 WO 2003016890 A2 WO2003016890 A2 WO 2003016890A2 DE 0202478 W DE0202478 W DE 0202478W WO 03016890 A2 WO03016890 A2 WO 03016890A2
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WO
WIPO (PCT)
Prior art keywords
measuring
internal resistance
exhaust gas
voltage
gas sensor
Prior art date
Application number
PCT/DE2002/002478
Other languages
German (de)
French (fr)
Other versions
WO2003016890A3 (en
Inventor
Erich Junginger
Dietmar Blessing
Christian Zimmermann
Wilhelm Haag
Frank Molwitz
Rene Schenk
Bernd Hilgenberg
Johann Riegel
Original Assignee
Robert Bosch Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Priority to JP2003521346A priority Critical patent/JP2004538487A/en
Priority to KR10-2003-7005184A priority patent/KR20040022411A/en
Priority to US10/399,152 priority patent/US6939037B2/en
Publication of WO2003016890A2 publication Critical patent/WO2003016890A2/en
Publication of WO2003016890A3 publication Critical patent/WO2003016890A3/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
    • G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
    • G01K7/20—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1493—Details
    • F02D41/1496—Measurement of the conductivity of a sensor

Definitions

  • the invention relates generally to temperature measurement in exhaust gas sensors, in particular of motor vehicles, and in particular to a method and a circuit for measuring the internal resistance of an electrochemical cell for determining the temperature of such an exhaust gas sensor.
  • the respective exhaust gas is measured and the amount of fuel supplied is corrected immediately in accordance with the measurement result, for example by means of the injection system.
  • the operation of the lambda probe is based on the principle of a galvanic oxygen concentration cell with a solid electrolyte.
  • Lambda probes designed as two-point probes are known to work according to the Nernst principle, on one Nernst cell based.
  • the solid electrolyte consists of two interfaces separated by a ceramic.
  • the ceramic material used becomes conductive at around 350 ° C for oxygen ions, so that when the oxygen content differs on both sides of the ceramic, the so-called Nernst voltage is generated. This electrical voltage is a measure of the difference in the oxygen content on both sides of the ceramic. Since the residual oxygen content in the exhaust a
  • the function and measuring accuracy of the lambda probes depends to a very high degree on the temperature of the measuring element, ie in the present case the Nernst cell. Due to changing exhaust gas temperatures and amounts, the probe temperature would fluctuate without further measures. As is known, the probe temperature is therefore kept as constant as possible, with regulated power being supplied to it with the aid of an electric heater. In order to determine the amount of heating power required in each case, a suitable measurement signal indicating the sensor temperature is required. The electrical signal is usually used as the measurement signal Internal resistance of the electrochemical Nernst cell is used. For this purpose, for example, a measuring current is impressed on the internal resistance and the voltage which is established is determined with the aid of an evaluation circuit.
  • the measuring current is preset by suitable dimensioning of the evaluation circuit.
  • tolerances that are usually present in the components of the evaluation circuit lead to errors when measuring the internal resistance mentioned and thus impair the control accuracy of the heating control.
  • the present invention is therefore based on the object of specifying a method mentioned at the outset and a circuit which avoid the aforementioned disadvantages and provide the highest possible measurement accuracy of a circuit for measuring the internal resistance of an exhaust gas sensor, with the aim of improving the control to a constant temperature and thus ultimately also improve the behavior of the exhaust gas sensor.
  • the invention proposes a special calibration method in which - preferably in combination with force / sense lines - temporarily or regularly switched to a reference resistor and the electrical voltage which then arises is stored in a memory. From now on, this stored voltage value serves as a reference value for measuring the actually desired value of the internal resistance R1.
  • the single figure shows a block diagram of a circuit according to the invention.
  • the circuit shown is used to measure the internal resistance (R1) 10 and thus indirectly to determine the temperature of a schematically illustrated Nernst cell 12 of an electrochemical exhaust gas sensor (not shown).
  • At 12 (ul) is here denotes the electrochemical source voltage of the Nernst cell.
  • the circuit consists of three circuit units, a measurement current generation unit 14, a measurement signal evaluation unit 16 and a switchover unit 18.
  • a voltage proportional to the resistance value of Rl is generated at Rl.
  • This voltage is then amplified by the measurement signal evaluation unit 16 and processed in such a way that an optimal detection of the measurement signal is made possible via an analog-digital (A / D) converter (not shown).
  • a / D converter (not shown).
  • the signal supplied by the A / D converter can then advantageously be further processed digitally.
  • the circuit shown and the method for its operation enable an improvement in accuracy only using standard electronic components.
  • an integration of the Switching using standard semiconductor processes enables.
  • the calibration resistor R2 and the changeover unit 18 having a plurality of changeover switches (Sl - S4).
  • the changeover of the measured values is switched over temporarily or at regular intervals to the known, precisely defined resistance R2 by means of the changeover switch S1 - S4.
  • the resistance value of R2 is expediently chosen so that it corresponds to the internal resistance R1 to be set - corresponding to the control point of the heating control.
  • the signal voltage UA which then arises at the output of the circuit is stored in a memory of a microcontroller (not shown) and from then on serves as a reference value for measuring the internal resistance R1.
  • This measure can thus eliminate circuit-related errors in the measuring current generating unit 14 and the measuring signal evaluation unit 16.
  • the accuracy of the output signal UA is therefore only determined by the accuracy of the calibration resistor R2.
  • the changeover unit 18 in the present exemplary embodiment is designed as a force / sense circuit.
  • the measuring current I_Mess 20 becomes Switched to measuring resistors Rl and R2 via switches S1 and S2 (force switches), to which only low accuracy requirements are required. Only the synchronization of all switches has to meet minimal requirements, which is usually easy to meet when the circuit is integrated, for example, in an Application Specific Integrated Circuit (ASIC).
  • ASIC Application Specific Integrated Circuit
  • the force / sense circuit is not absolutely necessary and can be dispensed with, for example, if the ratio of the resistance to be measured to the switch resistances is sufficiently large, e.g. when using low-resistance switches. The same also applies if the switches make significant contributions to the measured resistance value, but it is not important to the absolute value of the resistance to be measured, but only to come as close as possible to the comparison resistor R2.
  • the measurement signal is coupled into the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the measurement signal evaluation unit 16 via the
  • Measurement signal evaluation unit 16 the measurement signal is influenced only minimally. Therefore, relatively simple and inexpensive (high-resistance) switches can be used for S3 and S4. Measurement errors caused by the switches Sl ... S4 are eliminated by the calibration described using the resistor R2, as long as only S1 and S2 or S3 and S4 have comparable properties, for example an identical or similar on-state resistance.
  • inventive value circuit can also be advantageously used with two-line broadband lambda probes which are formed from a Nernst cell and a pump cell coupled to it.
  • the lambda probe and the evaluation circuit together provide a continuous lambda signal, by means of which lambda control can in principle be carried out at any operating point, i.e. also LAMBDA not equal to 1, is adjustable, and thus a "constant lambda control" is provided.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
  • Measuring Oxygen Concentration In Cells (AREA)

Abstract

The invention relates to a method and a circuit for measuring the internal resistance (R1) (10) of an electrochemical cell (12) in order to determine the temperature of an exhaust gas sensor, especially an exhaust gas sensor of a motor vehicle. The invention aims at achieving the highest possible measuring accuracy of a circuit for measuring the internal resistance of an exhaust gas sensor with the purpose of improving regulation to constant temperatures thereby ultimately improving the performance of the exhaust gas sensor. According to the invention, a measuring current (I_Mess) (20) is impressed upon the internal resistance (R1) (10) of the electrochemical cell (12) and the resulting first voltage is detected; switchover to a reference resistance (R2) is carried out temporarily or at regular time intervals and a second voltage resulting from switchover to the reference resistance (R2) is stored and then used as reference value to measure the internal resistance (R1) (10). Switchover (18) to the reference resistance (R2) is carried out e.g. by means of force/sense lines.

Description

Ermittlung der Temperatur eines Äbgassensαrs mittels kalibrierter Innenwiderstands essungDetermination of the temperature of an exhaust gas using calibrated internal resistance measurement
Beschreibungdescription
Die Erfindung betrifft allgemein die Temperaturmessung bei Abgassensoren insbesondere von Kraftfahrzeugen und im Speziellen ein Verfahren und eine Schaltung zur Messung des Innenwiderstandes einer elektrochemischen Zelle zur Ermittlung der Temperatur eines solchen Abgassensors .The invention relates generally to temperature measurement in exhaust gas sensors, in particular of motor vehicles, and in particular to a method and a circuit for measuring the internal resistance of an electrochemical cell for determining the temperature of such an exhaust gas sensor.
Eine Lambda-Regelung in Verbindung mit einem Katalysator ist heute das wirksamste Abgasreinigungsverfahren für den Ottomotor. Erst im Zusammenspiel mit derzeit verfügbaren Zünd- und Einspritzsystemen können sehr niedrige Abgaswerte erreicht werden. Besonders wirkungsvoll ist der Einsatz eines Dreiwege- oder Selektiv-Katalysators . Dieser Katalysatortyp hat die Eigenschaft, Kohlenwasserstoffe, Kohlenmonoxid und Stickoxide bis zu mehr als 98% abzubauen, falls der Motor in einem Bereich von etwa 1% um das stöchiometrische Luft-Kraftstoff-Verhältnis mit LAMBDA = 1 betrieben wird. Dabei gibt LAMBDA an, wieweit das tatsächliche vorhandene Luft-Kraftstoff- Gemisch von dem Wert LAMBDA = 1 abweicht, der einem zur vollständigen Verbrennung theoretisch notwendigen Massenverhältnis von 14,7 kg Luft zu 1 kg Benzin entspricht, d.h. LAMBDA ist der Quotient aus zugeführter Luftmasse und theoretischem Luftbedarf.Lambda control in conjunction with a catalytic converter is the most effective exhaust gas cleaning process for the gasoline engine today. Only in combination with currently available ignition and Injection systems can achieve very low emissions. The use of a three-way or selective catalyst is particularly effective. This type of catalytic converter has the property of reducing hydrocarbons, carbon monoxide and nitrogen oxides by up to more than 98% if the engine is operated in a range of approximately 1% around the stoichiometric air-fuel ratio with LAMBDA = 1. LAMBDA indicates the extent to which the actual air / fuel mixture deviates from the value LAMBDA = 1, which corresponds to a mass ratio of 14.7 kg air to 1 kg gasoline, which is theoretically necessary for complete combustion, ie LAMBDA is the quotient of the air mass supplied and theoretical air requirements.
Bei der Lambda-Regelung wird das jeweilige Abgas gemessen und die zugeführte Kraftstoffmenge entsprechend dem Messergebnis mittels bspw. des Einspritzsystems sofort korrigiert. Als Messfühler wird eine Lambda-Sonde verwendet, die exakt bei LAMBDA = 1 einen Spannungssprung aufweist und so ein Signal liefert, das anzeigt, ob das Gemisch fetter oder magerer als LAMBDA = 1 ist. Die Wirkungsweise der Lambda-Sonde beruht auf dem Prinzip einer galvanischen Sauerstoff-Konzentrationszelle mit einem Festkörperelektrolyt.With the lambda control, the respective exhaust gas is measured and the amount of fuel supplied is corrected immediately in accordance with the measurement result, for example by means of the injection system. A lambda probe is used as the sensor, which has a voltage jump exactly at LAMBDA = 1 and thus provides a signal that indicates whether the mixture is richer or leaner than LAMBDA = 1. The operation of the lambda probe is based on the principle of a galvanic oxygen concentration cell with a solid electrolyte.
Als Zweipunktsonden ausgeführte Lambda-Sonden arbeiten bekanntermaßen nach dem Nernst-Prinzip, auf einer Nernst-Zelle basierend. Der Festkörperelektrolyt besteht dabei aus zwei durch eine Keramik getrennte Grenzflächen. Das verwendete Keramikmaterial wird bei etwa 350° C für Sauerstoffionen leitend, so dass dann bei unterschiedlichem Sauerstoffanteil auf beiden Seiten der Keramik zwischen den Grenzflächen die sogenannte Nernstspannung erzeugt wird. Diese elektrische Spannung ist ein Maß für den Unterschied des Sauerstoff nteils zu beiden Seiten der Keramik. Da der Restsauerstoffgehalt im Abgas einesLambda probes designed as two-point probes are known to work according to the Nernst principle, on one Nernst cell based. The solid electrolyte consists of two interfaces separated by a ceramic. The ceramic material used becomes conductive at around 350 ° C for oxygen ions, so that when the oxygen content differs on both sides of the ceramic, the so-called Nernst voltage is generated. This electrical voltage is a measure of the difference in the oxygen content on both sides of the ceramic. Since the residual oxygen content in the exhaust a
Verbrennungsmotors in starkem Maße vom Luft-Kraftstoff- Verhältnis das dem Motor zugeführten Gemisches abhängig ist, ist es möglich, den Sauerstoffanteil im Abgas als Maß.für das tatsächlich vorliegende Luft-Kraftstoff- Verhältnis heranzuziehen.Internal combustion engine to a large extent on the air-fuel ratio which is dependent on the mixture supplied to the engine, it is possible to use the oxygen content in the exhaust gas as a measure of the actual air-fuel ratio.
Die Funktion und Messgenauigkeit der Lambda-Sonden ist in sehr hohem Maße von der Temperatur des Messelementes, d.h. vorliegend der Nernst-Zelle, abhängig. Durch wechselnde Abgastemperaturen und Abgasmengen bedingt würde die Sondentemperatur ohne weitere Maßnahmen starken Schwankungen unterliegen. Bekanntermaßen wird daher die Sondentemperatur möglichst konstant gehalten, wobei mit Hilfe eines elektrischen Heizers dieser geregelt Leistung zugeführt wird. Um die jeweils erforderliche Menge an Heizleistung zu ermitteln, wird ein geeignetes die Sensortemperatur angebendes Messsignal benötigt. ALs Messsignal wird in der Regel der elektrische Innenwiderstand der elektrochemischen Nernst-Zelle herangezogen. Dazu wird zum Beispiel ein Messstrom auf den Innenwiderstand aufgeprägt und d±e sich einstellende Spannung mit Hilfe einer Auswerteschaltung ermittelt.The function and measuring accuracy of the lambda probes depends to a very high degree on the temperature of the measuring element, ie in the present case the Nernst cell. Due to changing exhaust gas temperatures and amounts, the probe temperature would fluctuate without further measures. As is known, the probe temperature is therefore kept as constant as possible, with regulated power being supplied to it with the aid of an electric heater. In order to determine the amount of heating power required in each case, a suitable measurement signal indicating the sensor temperature is required. The electrical signal is usually used as the measurement signal Internal resistance of the electrochemical Nernst cell is used. For this purpose, for example, a measuring current is impressed on the internal resistance and the voltage which is established is determined with the aid of an evaluation circuit.
Der Messstrom wird dabei bekanntermaßen durch geeignete Dimensionierung der Auswerteschaltung voreingestellt. Nun führen bei den Bauteilen der Auswerteschaltung meist vorhandene Toleranzen zu Fehlereinflüssen bei der Messung des genannten Innenwiderstandes und beeinträchtigen somit die Regelgenauigkeit der Heizungsregelung.As is known, the measuring current is preset by suitable dimensioning of the evaluation circuit. Now, tolerances that are usually present in the components of the evaluation circuit lead to errors when measuring the internal resistance mentioned and thus impair the control accuracy of the heating control.
Der vorliegenden Erfindung liegt deshalb die Aufgabe zugrunde, ein eingangs genanntes Verfahren sowie eine Schaltung anzugeben, welche die vorgenannten Nachteile vermeiden und eine möglichst hohe Messgenauigkeit einer Schaltung zur Innenwiderstandsmessung eines Abgassensors bereitstellen, mit dem Ziel, die Regelung auf konstante Temperatur zu verbessern und damit letztlich auch das Verhalten des Abgassensors zu verbessern.The present invention is therefore based on the object of specifying a method mentioned at the outset and a circuit which avoid the aforementioned disadvantages and provide the highest possible measurement accuracy of a circuit for measuring the internal resistance of an exhaust gas sensor, with the aim of improving the control to a constant temperature and thus ultimately also improve the behavior of the exhaust gas sensor.
Diese Aufgabe wird gelöst durch die Merkmale der unabhängigen Ansprüche. Vorteilhafte Ausgestaltungen bzw. Weiterbildungen sind Gegenstand der Unteransprüche. Die Erfindung schlägt ein besonderes Kalibrierverfahren vor, bei dem - bevorzugt in Kombination mit Force/Sense-Leitungen - zeitweilig oder regelmäßig auf einen Referenzwiderstand umgeschaltet und die sich dann einstellende elektrische Spannung in einen Speicher abgelegt wird. Dieser abgelegte Spannungswert dient fortan als Referenzwert für die Messung des eigentlich gewünschten Wertes des Innenwiderstandes Rl .This object is achieved by the features of the independent claims. Advantageous refinements or developments are the subject of the dependent claims. The invention proposes a special calibration method in which - preferably in combination with force / sense lines - temporarily or regularly switched to a reference resistor and the electrical voltage which then arises is stored in a memory. From now on, this stored voltage value serves as a reference value for measuring the actually desired value of the internal resistance R1.
Durch diese Maßnahmen lässt sich die Messgenauigkeit einer Schaltung zur Innenwiderstandsmessung eines Abgassensors erhöhen. Das erfindungsgemäße Verfahren sowie die Schaltung begünstigen dabei insbesondere das Systemverhalten des Verbundes aus Abgassensor (z.B. Lambdasonde ) und der eingangs erwähnten Auswerteschaltung.These measures make it possible to increase the measuring accuracy of a circuit for measuring the internal resistance of an exhaust gas sensor. The method according to the invention and the circuit favor in particular the system behavior of the combination of exhaust gas sensor (e.g. lambda probe) and the evaluation circuit mentioned at the beginning.
Die Erfindung wird nachfolgend, unter Heranziehung der beigefügten Zeichnung, anhand einesThe invention is described below with reference to the accompanying drawing
Ausführungsbeispiels eingehender erläutert. Dabei zeigt die einzige Figur ein Blockschaltbild einer erfindungsgemäßen Schaltung.Embodiment explained in more detail. The single figure shows a block diagram of a circuit according to the invention.
Die gezeigte Schaltung dient zur Messung des Innenwiderstandes (Rl) 10 und damit indirekt zur Ermittlung der Temperatur einer schematisch dargestellten Nernst-Zelle 12 eines (nicht gezeigten) elektrochemischen Abgassensors. Mit 12 (Ul) ist hier die elektrochemische Quellspannung der Nernstzelle bezeichnet. Die Schaltung besteht aus drei Schaltungseinheiten, einer Messstromerzeugungseinheit 14, einer Messsignalauswertungseinheit 16 und einer Umschalteinheit 18.The circuit shown is used to measure the internal resistance (R1) 10 and thus indirectly to determine the temperature of a schematically illustrated Nernst cell 12 of an electrochemical exhaust gas sensor (not shown). At 12 (ul) is here denotes the electrochemical source voltage of the Nernst cell. The circuit consists of three circuit units, a measurement current generation unit 14, a measurement signal evaluation unit 16 and a switchover unit 18.
Mittels des erzeugten Messstromes (I_Mess) 20, welcher der Nernst-Zelle 12 aufgeprägt wird, wird an Rl eine zum Widerstandswert von Rl proportionale Spannung erzeugt. Diese Spannung wird anschließend durch die Messsignalauswertungseinheit 16 verstärkt und so aufbereitet, dass eine optimale Erfassung des Messsignals über einen (nicht gezeigten) Analog- Digital-(A/D)Wandler ermöglicht wird. Mittels des von dem A/D-Wandler gelieferten Signals kann dieses dann vorteilhaft digital weiterverarbeitet werden.Using the generated measuring current (I_Mess) 20, which is impressed on the Nernst cell 12, a voltage proportional to the resistance value of Rl is generated at Rl. This voltage is then amplified by the measurement signal evaluation unit 16 and processed in such a way that an optimal detection of the measurement signal is made possible via an analog-digital (A / D) converter (not shown). The signal supplied by the A / D converter can then advantageously be further processed digitally.
Etwa auftretende Toleranzen und Spannungsdriften sowohl in der Messstromerzeugungseinheit 14 als auch in der Messsignalauswertungseinheit 16 würden ohne besondere Maßnahmen als Fehler in das Ausgangssignal (UA) eingehen. Zur Erreichung einer hohen Genauigkeit des Rl-Signals müssten hochpräzise und somit teure Schaltungstechniken verwendet werden.Any tolerances and voltage drifts that occur both in the measuring current generating unit 14 and in the measuring signal evaluating unit 16 would enter the output signal (UA) as errors without special measures. In order to achieve a high accuracy of the R1 signal, high-precision and therefore expensive circuit techniques would have to be used.
Die gezeigte Schaltung sowie das Verfahren zu ihrem Betrieb ermöglichen eine Genauigkeitsverbesserung ausschließlich unter Verwendung von elektronischen Standardkomponenten. Zudem wird eine Integration der Schaltung mittels Standard-Halbleiterprozessen ermöglicht.The circuit shown and the method for its operation enable an improvement in accuracy only using standard electronic components. In addition, an integration of the Switching using standard semiconductor processes enables.
Dazu dienen zum einen der Kalibrierwiderstand R2 und die mehrere Umschalter (Sl - S4) aufweisende Umschalteinheit 18. Mittels der Umschalter Sl - S4 wird die Messwerterfassung zeitweilig oder in regelmäßigen Zeitabständen auf den bekannten, präzise definierten Widerstand R2 umgeschaltet. Der Widerstandswert von R2 wird dabei zweckmäßigerweise so gewählt, dass er dem einzustellenden Innenwiderstand Rl - entsprechend dem Regelpunkt der Heizungsregelung - entspricht. Die sich dann am Ausgang der Schaltung einstellende Signalspannung UA wird in einen Speicher eines (nicht gezeigten) Mikrocontrollers abgelegt und dient fortan als Referenzwert für die Messung des Innenwiderstandes Rl.This is done on the one hand by the calibration resistor R2 and the changeover unit 18 having a plurality of changeover switches (Sl - S4). The changeover of the measured values is switched over temporarily or at regular intervals to the known, precisely defined resistance R2 by means of the changeover switch S1 - S4. The resistance value of R2 is expediently chosen so that it corresponds to the internal resistance R1 to be set - corresponding to the control point of the heating control. The signal voltage UA which then arises at the output of the circuit is stored in a memory of a microcontroller (not shown) and from then on serves as a reference value for measuring the internal resistance R1.
Durch diese Maßnahme können somit schaltungsbedingte Fehler in der Messstromerzeugungseinheit 14 und der Messsignalauswertungseinheit 16 eliminiert werden. Die Genauigkeit des Ausgangssignales UA wird somit nur noch durch die Genauigkeit des Kalibrierwiderstandes R2 bestimmt .This measure can thus eliminate circuit-related errors in the measuring current generating unit 14 and the measuring signal evaluation unit 16. The accuracy of the output signal UA is therefore only determined by the accuracy of the calibration resistor R2.
Um des Weiteren Fehler durch die Umschalter Sl - S4 selbst zu eliminieren, ist die Umschalteinheit 18 in dem vorliegenden Ausführungsbeispiel als Force/Sense- Schaltung ausgelegt. Der Messstrom I_Mess 20 wird dabei über Schalter Sl und S2 (Force-Schalter), an die nur geringe Genauigkeitsanforderungen zu stellen sind, auf die Messwiderstände Rl bzw. R2 geschaltet. Lediglich der Gleichlauf sämtlicher Schalter hat minimalen Anforderungen zu genügen, was bei einer Integration der Schaltung bspw. in einen Application Specific Integrated Circuit (ASIC) in der Regel einfach zu erfüllen ist.In order to further eliminate errors caused by the changeover switches S1-S4 itself, the changeover unit 18 in the present exemplary embodiment is designed as a force / sense circuit. The measuring current I_Mess 20 becomes Switched to measuring resistors Rl and R2 via switches S1 and S2 (force switches), to which only low accuracy requirements are required. Only the synchronization of all switches has to meet minimal requirements, which is usually easy to meet when the circuit is integrated, for example, in an Application Specific Integrated Circuit (ASIC).
Es ist hervorzuheben, dass die Force/Sense-Schaltung nicht zwingend erforderlich ist und auf diese bspw. dann verzichtet werden kann, wenn das Verhältnis des zu messenden Widerstandes zu den Schalterwiderständen ausreichend groß ist, so z.B. bei Verwendung niederohmiger Schalter. Gleiches gilt auch, wenn die Schalter zwar nennenswerte Beiträge zum gemessenen Widerstandswert liefern, es aber nicht auf den Absolutwert des zu messenden Widerstandes ankommt, sondern nur darauf, dem vorliegenden Vergleichswiderstand R2 möglichst nahe zu kommen.It should be emphasized that the force / sense circuit is not absolutely necessary and can be dispensed with, for example, if the ratio of the resistance to be measured to the switch resistances is sufficiently large, e.g. when using low-resistance switches. The same also applies if the switches make significant contributions to the measured resistance value, but it is not important to the absolute value of the resistance to be measured, but only to come as close as possible to the comparison resistor R2.
Die Einkopplung des Messsignals in die Messsignalauswertungseinheit 16 geschieht über die beiden Schalter S3 und S4 (Sense-Schalter). Aufgrund des hochohmigen Einganges derThe measurement signal is coupled into the measurement signal evaluation unit 16 via the two switches S3 and S4 (sense switch). Due to the high-impedance input of the
Messsignalauswertungseinheit 16 wird das Messsignal nur minimal beeinflusst. Deswegen können für S3 und S4 relativ einfache und kostengünstige (hochohmige) Schalter verwendet werden. Durch die Schalter Sl ... S4 bedingte Messfehler werden durch die beschriebene Kalibrierung mittels des Widerstandes R2 eliminiert, solange nur Sl und S2 bzw. S3 und S4 vergleichbare Eigenschaften, z.B. einen gleichen oder ähnlichen Durchschaltwiderstand, aufweisen.Measurement signal evaluation unit 16, the measurement signal is influenced only minimally. Therefore, relatively simple and inexpensive (high-resistance) switches can be used for S3 and S4. Measurement errors caused by the switches Sl ... S4 are eliminated by the calibration described using the resistor R2, as long as only S1 and S2 or S3 and S4 have comparable properties, for example an identical or similar on-state resistance.
Es ist schließlich anzumerken, dass die erfindungsgemäße Aμswerteschaltung auch bei zweizeiligen Breitband-Lambdasonden vorteilhaft einsetzbar ist, welche aus einer Nernstzelle und einer mit dieser gekoppelten Pumpzelle gebildet sind. Dabei stellen die Lamda-Sonde und die Auswerteschaltung zusammen ein kontinuierliches Lambda-Signal bereit, mittels dessen eine Lambda-Regelung prinzipiell auf jeden beliebigen Arbeitspunkt, d.h. auch LAMBDA ungleich 1, einstellbar ist, und somit eine " stetige Lambda-Regelung" bereitgestellt wird. Finally, it should be noted that the inventive value circuit can also be advantageously used with two-line broadband lambda probes which are formed from a Nernst cell and a pump cell coupled to it. The lambda probe and the evaluation circuit together provide a continuous lambda signal, by means of which lambda control can in principle be carried out at any operating point, i.e. also LAMBDA not equal to 1, is adjustable, and thus a "constant lambda control" is provided.

Claims

AnsprücheExpectations
Verfahren zur Messung des Innenwiderstandes Rl (10) einer elektrochemischen Zelle (12) zur Ermittlung der Temperatur eines die elektrochemische Zelle aufweisenden Abgassensors insbesondere eines Kraftfahrzeuges, dadurch gekennzeichnet, dass dem Innenwiderstand Rl (10) der elektrochemischen Zelle (12) ein Messstrom I_Mess (20) aufgeprägt wird und eine sich ergebende erste Spannung erfasst wird, dass zeitweilig oder in regelmäßigen Zeitabständen auf einen Referenzwiderstand R2 umgeschaltet wird und dass eine bei der Umschaltung auf den Referenzwiderstand R2 sich durch den Messstrom ergebende zweite Spannung gespeichert und danach als Referenzwert für die Messung des Innenwiderstandes Rl (10) herangezogen wird.Method for measuring the internal resistance R1 (10) of an electrochemical cell (12) for determining the temperature of an exhaust gas sensor having the electrochemical cell, in particular of a motor vehicle, characterized in that the internal resistance R1 (10) of the electrochemical cell (12) has a measuring current I_Mess (20 ) is impressed and a resulting first voltage is recorded, that a switch is made to a reference resistor R2 temporarily or at regular intervals and that a second voltage resulting from the measuring current when switching to the reference resistor R2 is stored and then as a reference value for measuring the Internal resistance Rl (10) is used.
Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Umschaltung auf den Referenzwiderstand R2 mittels Force/Sense-Leitungen erfolgt.A method according to claim 1, characterized in that the switchover to the reference resistor R2 takes place by means of force / sense lines.
Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass ein am Innenwiderstand Rl sich ergebendes Spannungssignal mittels einer Messsignalauswertungseinheit (16) verstärkt und/oder aufbereitet wird.A method according to claim 1 or 2, characterized in that a voltage signal resulting at the internal resistance Rl by means of a Measuring signal evaluation unit (16) is amplified and / or processed.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass das verstärkte und/oder aufbereitete Spannungssignal einem Analog-Digital-Wandler zugeführt wird.4. The method according to claim 3, characterized in that the amplified and / or conditioned voltage signal is fed to an analog-to-digital converter.
5. Verfahren nach einem der Ansprüche 2 bis 4, dadurch gekennzeichnet, dass der Messstrom I_Mess (20) mittels Forceschaltern Sl, S2 auf die Messwiderstände Rl und R2 geschaltet wird und dass die Einkopplung der erfassten Messspannung in die Messsignalauswertungseinheit (16) über Senseschalter S3, S4 erfolgt.5. The method according to any one of claims 2 to 4, characterized in that the measuring current I_Mess (20) is switched by means of force switches S1, S2 to the measuring resistors R1 and R2 and that the coupling of the detected measuring voltage into the measuring signal evaluation unit (16) via sensor switch S3 , S4 takes place.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, dass die Schalter Sl und S2 sowie die Schalter S3 und S4 einen gleichen oder ähnlichen Durchschaltwiderstand aufweisen.6. The method according to claim 5, characterized in that the switches S1 and S2 and the switches S3 and S4 have the same or similar on-resistance.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der Widerstandswert von R2 so gewählt wird, dass er dem einzustellenden Innenwiderstand Rl ' im Wesentlichen entspricht.7. The method according to any one of the preceding claims, characterized in that the resistance value of R2 is selected so that it essentially corresponds to the internal resistance Rl ' to be set.
8. Schaltung zur Messung des Innenwiderstandes Rl (10) einer elektrochemischen Zelle (12) zur Ermittlung der Temperatur eines Abgassensors insbesondere eines Kraftfahrzeuges, gekennzeichnet durch Schaltungsmittel zur Ausführung des Verfahrens nach einem der vorhergehenden Ansprüche.8. Circuit for measuring the internal resistance R1 (10) of an electrochemical cell (12) Determination of the temperature of an exhaust gas sensor, in particular of a motor vehicle, characterized by switching means for executing the method according to one of the preceding claims.
9. Schaltung nach Anspruch 8, gekennzeichnet durch einen Referenzwiderstand R2, eine mehrere Umschalter (Sl - S4) aufweisende Umschalteinheit (18), wobei mittels der Umschalter (Sl - S4) die Messwerterfassung zeitweilig oder regelmäßig auf den Referenzwiderstand R2 umschaltbar ist.9. A circuit according to claim 8, characterized by a reference resistor R2, a switch unit (18) having a plurality of changeover switches (Sl - S4), the measured value acquisition being able to be switched temporarily or regularly to the reference resistor R2 by means of the changeover switch (Sl - S4).
10. Schaltung nach Anspruch 8 oder 9, gekennzeichnet durch eine Messstromerzeugungseinheit (14) und eine Messsignalauswertungseinheit (16), wobei die Umschaltung des Messstroms I_Mess (20) auf die Messwiderstände Rl und R2 und die Einkopplung einer erfassten Messspannung in die Messsignalauswertungseinheit (16) mittels Force/Sense Leitungen erfolgt. 10. The circuit according to claim 8 or 9, characterized by a measuring current generating unit (14) and a measuring signal evaluation unit (16), wherein the switching of the measuring current I_Mess (20) to the measuring resistors R1 and R2 and the coupling of a detected measuring voltage into the measuring signal evaluation unit (16) using force / sense lines.
PCT/DE2002/002478 2001-08-14 2002-07-06 Determining the temperature of an exhaust gas sensor by means of calibrated internal resistance measurement WO2003016890A2 (en)

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